HP 49g+ - Manual (Page 170)

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base to be used for binary integers, choose either HEX(adecimal), DEC(imal),
OCT(al), or BIN(ary) in the BASE menu. For example, if
@HEX ! is selected,
binary integers will be a hexadecimal numbers, e.g., #53, #A5B, etc. As
different systems are selected, the numbers will be automatically converted to
the new current base.
To write a number in a particular system, start the number with # and end
with either h (hexadecimal), d (decimal), o (octal), or b (binary), examples:
HEX
DEC
OCT
BIN
Reference
For additional details on numbers from different bases see Chapter 19 in the
calculator’s User’s Guide.